Three-dimensional Visualization And Mechanical Characterization Of Skeleton Structure Of Asphalt Mixture Based On Detection Of Aggregate Contacts

Asphalt mixture comprises of aggregates,asphalt,and air voids.Aggregates accounts for more than 90% of the mass of the mixture.Coarse aggregates in contact make up the skeleton structure of the mixture,which bear and transfer the external loads.In other words,the skeleton structure significantly affects the deformation resistance of the mixture.Morphological characterization and evaluation of the skeleton structure help to investigate the correlation between the morphological properties of the skeleton and mixture stability.To achieve this goal,realistic aggregates were three-dimensional(3-D)reconstructed using computer graphics and image processing techniques from Computed Tomography(CT)imaging.Subsequently,the algorithm for contact detection was developed to further form the contact network of aggregates.The skeleton structure was then identified to evaluate its morphology.Furthermore,the morphological evolution of the skeleton was characterized during loading.The correlation between morphological evaluation and stability of the skeleton was also analyzed and validated.The main work is as follows.(1)More than 3,000 coarse aggregates were reconstructed from CT-scanned specimens(a cylindrical container full of aggregates and three samples cut from a field core)to detect aggregate contacts.(2)Surface triangles were extracted from the tetrahedral mesh of an aggregate obtained in ANSYS,and properties of 3-D aggregate contacts were then determined.Specifically,the area,and normal vectors of contact regions were calculated to obtain the contact network of aggregates represented using directed weighted graphs.The larger weight of an edge in the graph,the better of load transfer effect will be.The effective paths of load transfer were identified in the graph,and paths in connection constitute a force chain.Force chains constitute the skeleton structure.Furthermore,the morphological indices of the skeleton were proposed and quantified.Three virtual specimens were obtained by progressive removal of aggregates in a cylindrical container.Three simulations of uniaxial compression tests were conducted using finite element method.Results indicate that the proposed indices agree well with the deformation resistance,distributional characteristics of stress and strain of mixtures.(3)The evaluation indices for the initial morphology of skeleton were improved with a deeper morphological characterization of force chains taken into consideration.Based on the new morphological indices,the evolutional characterization of the skeleton during loading was quantified by topological and nontopological difference in skeleton morphology.Three samples cut from a field core were reconstructed to evaluate the initial morphology of the skeleton.Simulations of uniaxial compression tests of the three samples were conducted.The topological and nontopological difference in skeleton morphology,strain energy of aggregates,and stress distribution on contact regions of aggregates were extracted at four time points,namely 7.5s,15 s,22.5s,and 30 s in simulation.Based on that,the mixture stability was comprehensively evaluated to analyze the correlation between it and morphological indices of the skeleton.Results suggest that the evaluation of initial skeleton agrees well with the deformation resistance of samples,which also prove the reliability of the prediction for deformation resistance of the mixture using the approach proposed in this paper.